We are investigating the role of hypersensitivity to viruses by measurement of virus specific IgE antibody against viruses isolated from and detected in SIDS cases and by searching for histologic and biochemical evidence of hypersensitivity reactions. Isolation and detection of viruses are being done by a) direct isolation (CPE), b) intrinsic interference, and c) immunofluorescent antibody. Measurements include 1) neutralizing antibody titers in serum and bronchial washings against viruses isolated, 2) total IgE protein in serum and of IgE and IgA in bronchial washings, 3) virus specific IgE in serum and of virus specific IgE and IgA in bronchial washings, 4) total histamine content of lung samples, 5) interferon in bronchial washings and cerebrospinal fluid. Study of total histologic sections of lung, bronchi, trachea, and larynx are being performed to determine if morphologic changes in the tissue mast cells are present.